1. Field of the Invention
The present invention relates to an anesthetic reflector of the type allowing re-use of exhaled anesthetic agents in inhalation anesthesia.
2. Description of the Prior Art
Anesthetic reflectors for the re-use of gas-borne anesthetic agents are well known and are described in, for example, U.S. Pat. Nos. 5,044,361 and 5,471,979. These reflectors generally have a housing in which there is provided openings that delimit a common gas flow channel through the interior of the housing. Retained within the housing and disposed internally the gas flow channel is a filter for the alternating sorption and desorption of anesthetic agent from and into gas passing along the common flow channel. In use, these anesthetic reflectors are located within pneumatic circuits of anesthetic ventilator systems so that anesthetic-rich expiration gas, which is exhaled by a patient into the pneumatic circuit during an expiration phase of a patient breathing cycle, passes along the common flow channel and through the filter in one flow direction and so that inspiration gas in the pneumatic circuit, which is to be supplied to the patient during a subsequent inspiration phase of the patient breathing cycle, passes along the common flow channel, usually but not necessarily in the opposite flow direction, and through the filter. The filter acts to retain anesthetic agent borne by the expiration gas and then to release this retained anesthetic agent into the inspiration gas for re-supply (reflection) to the patient.
One problem with these known reflectors is that the common flow channel constitutes a “dead-space” in which carbon dioxide (CO2), that is also exhaled by the patient, remains after an expiration phase, and therefore may be undesirably re-supplied to the patient with the inspiration gas.
In order to overcome this problem it is known to provide an additional filter for retaining CO2 in inspiration gas passing from the anesthetic gas reflector. Such a CO2 filter may be integral with the reflector or may be a separate unit.
A further problem with the known reflectors is that in order to be able to quickly reduce the anesthetic concentration in the inspiration gas that otherwise would pass through the reflector, an additional gas flow line and associated flow controller are required by which the anesthetic sorption filter may be selectively by-passed. It is further known to realize this by-pass line as a separate flow channel within the housing of the reflector.